Switchable multi perspective detector, optics therefore and method of operating thereof

ABSTRACT

A secondary charged particle detection device for detection of a signal beam is described. The device includes a detector arrangement having at least two detection elements with active detection areas, wherein the active detection areas are separated by a gap (G), a particle optics configured for separating the signal beam into a first portion of the signal beam and into at least one second portion of the signal beam, and configured for focusing the first portion of the signal beam and the at least one second portion of the signal beam. The particle optics includes an aperture plate and at least a first inner aperture openings in the aperture plate, and at least one second radially outer aperture opening in the aperture plate, wherein the first aperture opening has a concave shaped portion, particularly wherein the first aperture opening has a pincushion shape.

FIELD

Embodiments of the invention relate to charged particle beam devices,for example, for inspection system applications, testing systemapplications, lithography system applications, defect review or criticaldimensioning applications or the like. It also relates to methods ofoperation thereof. Further, embodiments of the invention relates toapplications having a charged particle path for secondary particles,e.g. for electron beam inspection (EBI). Specifically, embodiment of theinvention relates to charged particle units, to charged particledetection devices, a charged particle beam device, a charged particlemulti-beam device and methods of operating theses devices.

BACKGROUND

Charged particle beam apparatuses have many functions in a plurality ofindustrial fields, including, but not limited to, inspection ofsemiconductor devices during manufacturing, exposure systems forlithography, detecting devices and testing systems. Thus, there is ahigh demand for structuring and inspecting specimens within themicrometer and nanometer scale.

Micrometer and nanometer scale process control, inspection orstructuring, is often done with charged particle beams, e.g. electronbeams, which are generated and focused in charged particle beam devices,such as electron microscopes or electron beam pattern generators.Charged particle beams offer superior spatial resolution compared to,e.g. photon beams due to their short wavelengths.

Besides resolution, throughput is an issue of such devices. Since largesubstrate areas have to be patterned or inspected, throughput of, forexample, larger than 10 cm²/min is desirable. In charged particle beamdevice, the throughput depends quadratically on the image contrast.Thus, there is a need for contrast enhancement.

Particle detectors, e.g. electron detectors, for particle beam systems,e.g. electron microscopes can be used for electron beam inspection(EBI), defect review (DR) or critical dimension (CD) measurement,focused ion Beam systems (FIB) or the like. Upon irradiation of a sampleby a primary beam of electrons, secondary particles, e.g. secondaryelectrons (SE), are created, which carry information about thetopography of the sample, its chemical constituents, its electrostaticpotential and others. In the simplest detectors, all of the SE arecollected and lead to a sensor, usually a scintillator, a pin diode orthe like. An image is created where the gray level is proportional tothe number of electrons collected.

High resolution electron optics systems require a short working distancebetween the objective lens and the wafer. Secondary electron collectionis therefore typically done inside the column above the objective lens.A configuration commonly found in prior-art electron-beam imagingsystems is shown schematically in FIG. 1. A column with length 104,including an emitter 105, an objective lens 10 and an annularsecondary-electron detector 115, are spaced at a working distance 120from a specimen 125. Primary electron beam 130 from emitter 105 isdirected at specimen 125 through an opening 135 in annular detector 115.Secondary electrons 140 are emitted from specimen 125 in a broad conesurrounding primary beam 130. Some of secondary electrons 140 arecollected by detector 115 to produce a secondary-electron (SE) signal145.

Further, it is desired for many applications that the imaginginformation is increased while high-speed detection is provided. Forexample, upon irradiation of a sample by a primary beam of electrons,secondary electrons (SE) are created which carry information about thetopography of the sample, its chemical constituents, its electrostaticpotential and others. High speed detection provided with topographyinformation and/or information on the energy of the secondary particlesis a challenging task, for which continuous improvement is desired.Accordingly, improvements of the detection in the SEM-based tools,particularly in high throughput defect inspection or review tools aredesired. Additionally or alternatively, separation of several signalbeam bundles, e.g. with reduced cross-talk, is desired for detection oftopography imaging or the like.

SUMMARY

According to one embodiment, a secondary charged particle detectiondevice for detection of a signal beam is provided. The device includes adetector arrangement having at least two detection elements with activedetection areas, wherein the active detection areas are separated by agap, a particle optics configured for separating the signal beam into afirst portion of the signal beam and into at least one second portion ofthe signal beam, and configured for focusing the first portion of thesignal beam and the at least one second portion of the signal beam. Theparticle optics includes an aperture plate and at least a first apertureopening in the aperture plate, and at least one second aperture openingin the aperture plate, wherein the first aperture opening has a concaveshaped portion.

According to another embodiment, a charged particle beam device isprovided. The device includes a charged particle beam source forproviding a primary charged particle beam, a first focusing element forfocusing the primary charged particle beam on the specimen, wherein asignal beam is generated, and a charged particle detection device. Thedetection device includes a detector arrangement having at least twodetection elements with active detection areas, wherein the activedetection areas are separated by a gap, a particle optics configured forseparating the signal beam into a first portion of the signal beam andinto at least one second portion of the signal beam, and configured forfocusing the first portion of the signal beam and the at least onesecond portion of the signal beam. The particle optics includes anaperture plate and at least a first aperture opening in the apertureplate, and at least one second aperture opening in the aperture plate,wherein the first aperture opening has a concave shaped portion.

According to a further embodiment, charged particle multi-beam device isprovided. The charged particle multi-beam device includes at least twocharged particle beam devices. Each of the two devices includes acharged particle beam source for providing a primary charged particlebeam, a first focusing element for focusing the primary charged particlebeam on the specimen, wherein a signal beam is generated, and a chargedparticle detection device. The detection device includes a detectorarrangement having at least two detection elements with active detectionareas, wherein the active detection areas are separated by a gap, aparticle optics configured for separating the signal beam into a firstportion of the signal beam and into at least one second portion of thesignal beam, and configured for focusing the first portion of the signalbeam and the at least one second portion of the signal beam. Theparticle optics includes an aperture plate and at least a first apertureopening in the aperture plate, and at least one second aperture openingin the aperture plate, wherein the first aperture opening has a concaveshaped portion.

According to another embodiment, a method of operating a detectiondevice is provided. The method includes biasing an aperture plate of aparticle optics, wherein the particle optics includes at least a firstaperture opening (202) in the aperture plate, and at least one secondaperture opening in the aperture plate, wherein the aperture plate isbiased such that one potential is surrounding the first aperture openingand wherein the first aperture opening has a concave shaped portion, anddetecting a signal beam with a detector assembly having at least onedetection element corresponding to the first aperture opening and atleast one detection element corresponding to the at least one secondaperture opening.

Embodiments are also directed at apparatuses for carrying out thedisclosed methods and include apparatus parts for performing eachdescribed method step. These method steps may be performed by way ofhardware components, a computer programmed by appropriate software, byany combination of the two or in any other manner. Furthermore,embodiments according to the invention are also directed at methods bywhich the described apparatus operates. It includes method steps forcarrying out every function of the apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments. The accompanying drawings relate to embodiments of theinvention and are described in the following:

FIG. 1 shows schematically a detection scheme according to the state ofthe art;

FIGS. 2A and 2B illustrate a secondary particle optics and a detectionassembly according to embodiments described herein;

FIG. 2C illustrates a view of a detector arrangement according toembodiments described herein;

FIG. 2D illustrates a secondary particle optics and a detection assemblyaccording to embodiments described herein;

FIG. 2E illustrate a secondary particle optics according to embodimentsdescribed herein;

FIG. 3A illustrates a secondary particle optics and a detection assemblyaccording to embodiments described herein;

FIG. 3B illustrates a secondary particle optics and a yet furtherdetection assembly according to embodiments described herein;

FIG. 4 illustrates a secondary particle optics having an aperture plate;

FIG. 5 illustrates a secondary particle optics having an aperture plateaccording to embodiments described herein, wherein the central openinghas concave portions, i.e. pincushion shape;

FIGS. 6A and 6B illustrate further embodiments relating to an apertureplate and biasing thereof;

FIG. 7A shows a schematic view of a system, which can be utilized for asecondary particle optics and a detection assembly according toembodiments described herein and having a Wien filter type separatingunit;

FIGS. 7B to 7D show schematically other beam paths that may be realizedwith a Wien filter type separating unit;

FIG. 8A shows a schematic view of embodiments, which can be utilized fora secondary particle optics and a detection assembly according toembodiments described herein, and having a magnetic dipole beamseparating unit;

FIGS. 8B to 8D show schematically other beam paths that may be realizedwith a magnetic dipole beam separating unit;

FIGS. 9A and 9B show schematic side views of charged particle unitsaccording to embodiments described herein;

FIG. 9C shows a schematic side view of a charged particle beam devicehaving a secondary particle optics and a detection assembly according toembodiments described herein;

FIG. 10 shows a schematic side view of a charged particle beam deviceaccording embodiments described herein;

FIG. 11 shows a schematic side view of a charged particle multi-beamdevice according to embodiments described herein; and

FIG. 12 shows a schematic side view of a charged particle multi-beamdevice according embodiments described herein.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference will now be made in detail to the various embodiments of theinvention, one or more examples of which are illustrated in the figures.Within the following description of the drawings, the same referencenumbers refer to same components. Generally, only the differences withrespect to individual embodiments are described. Each example isprovided by way of explanation of the invention and is not meant as alimitation of the invention. Further, features illustrated or describedas part of one embodiment can be used on or in conjunction with otherembodiments to yield yet a further embodiment. It is intended that thedescription includes such modifications and variations.

Without limiting the scope of protection of the present application, inthe following the charged particle beam device or components thereofwill exemplarily be referred to as a charged particle beam deviceincluding the detection of secondary electrons. Embodiments of thepresent invention can still be applied for apparatuses and componentsdetecting corpuscles, such as secondary and/or backscattered chargedparticles in the form of electrons or ions, photons, X-rays or othersignals in order to obtain a specimen image. Generally, when referringto corpuscles they are to be understood as light signals in which thecorpuscles are photons as well as particles, in which the corpuscles areions, atoms, electrons or other particles.

As describe herein, discussions and descriptions relating to thedetection are exemplarily described with respect to electrons inscanning electron microscopes. However, other types of chargedparticles, e.g. positive ions, could be detected by the device in avariety of different instruments.

According to embodiments herein, which can be combined with otherembodiments, a signal beam is referred to a beam of secondary particlesor a secondary beam, i.e. secondary and/or backscattered particles.Typically, the signal beam or secondary beam is generated by theimpingement of the primary beam on a specimen. A primary beam isgenerated by a charged particle beam source and is guided and deflectedon a specimen to be inspected or imaged.

A “specimen” as referred to herein, includes, but is not limited to,semiconductor wafers, semiconductor workpieces, and other workpiecessuch as memory disks and the like. Embodiments of the invention may beapplied to any workpiece on which material is deposited or which isstructured. A specimen includes a surface to be structured or on whichlayers are deposited, an edge, and typically a bevel. According to someembodiments, which can be combined with other embodiments describedherein, the apparatus and methods are configured for or are applied forelectron beam inspection, for critical dimensioning applications anddefect review applications

Generally, when referring to focusing a charged particle beam, it isunderstood that the beam of charged particles is reduced in divergence.This means, the charged particles of a beam are focused or at leastcollimated towards a subsequent beam optical element to decrease lossesof charged particles due to divergence or due to blocking of chargedparticles. Correspondingly, defocusing is understood as increasing thedivergence.

For EBI applications, a bright field (BF) detector, as described above,is used, but it is not sensitive enough to changes in topography orsurface potential (voltage contrast—VC). VC can be enhanced by energyfiltering the SE signal, while topography information resulting fromphysical defects can be enhanced by using multiple sensors that collectonly SE within certain ranges of take-off angles at the sample.According to typical embodiments, which can be combined with otherembodiments described herein, topography detectors can be divided into 4or more segments (with or without a central BF area) which can be readseparately. The signals can then be combined (e.g. subtracted) toenhance contrast. For meaningful multi perspective imaging, includingenergy or angular filtering, the information carried by the SE needs tobe conserved while the beam is transferred from the sample to thesensor. Thus, according to embodiments described herein, an opticalsystem (SE optics) is provided. According to some embodiments, the SEoptics can include a beam splitter that separates the primary beam andthe SE bundle, one or more SE focus lenses, and alignment deflectors.

For defect inspection tools and review tools or critical dimensioningtools an enhanced contrast, for example topography, can be generated bydetecting secondary particles depending on their starting angle.Thereby, enhanced contrast of the inspected features and/or defects canbe obtained. For detection of the secondary particle beam depending onthe starting angle, separation of the secondary beam to individualdetection elements or detection is provided. However, particularly forhigh-speed detection applications, as referred to in embodimentsdescribed herein, manufacturing of a sensor with individual segments,which are closely packed without dead area between them, i.e. which donot have a significant gap between the sensor elements, is difficult.

Particularly for EBI applications, high throughput is desired, whichresults in the need for extremely fast sensors. Accordingly, PIN diodescan be used. However, the obtainable bandwidth depends on the size ofthe diode, and a sensor area 1 mm² or below is typically utilized.Accordingly, the dead areas in a detector arrangement are increased ifthe detection speed is increased.

Embodiments described herein provide a detector arrangement and asecondary beam optics, which allows for high-speed topographymeasurements. Some embodiments described herein provide a high speeddetector that allows further to easily switch between BF imaging,wherein all SE reach a single detector, and topographic imaging, whereinat least 2 sensors, typically at least 4 sensors for the 4 quadrants oflarge starting angles are provided. Additionally, a central detector forlow angle SE can be provided. According to some embodiments, which canbe combined with other embodiments described herein, in both imagingmodes the SE can also be filtered according to their energy, such thatonly SE with an energy above a certain threshold reach the sensor, i.e.the detector arrangement.

According to an embodiment, which can be combined with other embodimentsdescribed herein a secondary charged particle detection device fordetection of a signal beam is provided. The device includes a detectorarrangement having at least two detection elements with active detectionareas, wherein the active detection areas are separated by a gap, aparticle optics configured for separating the signal beam into a firstportion of the signal beam and into at least one second portion of thesignal beam, and configured for focusing the first portion of the signalbeam and the at least one second portion of the signal beam. Theparticle optics includes an aperture plate and at least a first inneraperture opening in the aperture plate, and at least one second,radially outer aperture opening in the aperture plate, wherein theaperture plate is configured to be biased to one potential surroundingthe first aperture opening and the at least one second aperture opening.

FIG. 2A shows a detector arrangement 220, with detection elements 222.As can be seen in FIGS. 2A and 2C, the detection elements 222 areseparated from each other by a gap between the detection elements 222.The detection elements 222 are supported by a holder 224 of the detectorarrangement 220.

According to typical embodiments, which can be combined with otherembodiments described herein, the separation, i.e. the gap between thedetection elements 222, has at least the same length in thecorresponding dimension as the active area of the detection elements222. According to typical embodiments, the gap can be in a range of 1 mmto 10 mm. A typical ratio G/L of the gap and the corresponding length ofactive area, which can be utilized alternatively or additionally to theabove-mentioned gap dimension, can be 1 or above and 7 or below.

According to yet further embodiments, which can be combined with otherembodiments described herein, the detection elements 222 can bePIN-diodes, which are used as the sensor for detecting secondaryparticles, for example secondary electrons. According to yet furtherembodiments, which can be combined with other embodiments describedherein, the devices and methods for separation of the signal beamtraveling along optical axis 2, can also be utilized for otherdetectors, e.g. detector assemblies including scintillators, avalanchephoto diodes (APD), or the like.

As described herein, secondary particles or secondary electrons areunderstood as either backscattered particles/electrons orparticles/electrons, which are generated due to impingement of theprimary charged particle beam on the specimen.

PIN-Diodes can be used for high-speed detection applications in light oftheir large bandwidth, for example in the range of 1 to 10 GHz or 2 GHzor above. Thereby, the active area of the Pin-diodes limits thedetection speed. That is, the larger the active area of the pin diode,the slower the detection speed. Accordingly, the active area of the pindiodes is reduced to an area of 1 mm² or below, in order to provide thedesired detection speed of 2 GHz or above. The size of the active areaof the detection element 222 delimits the ratio of the detection area ascompared to the gaps there in-between. Accordingly, the detectorarrangement 220 having a desired bandwidth for high-speed detection isprovided with the gaps between the active areas of the detectionelements. Accordingly, a spatial separation, which is dictated by thedesign of the detection elements 222, is given.

According to embodiments described herein, a secondary particle optics200 is provided. As shown in FIGS. 2A and 2B, the particle optics 200includes at least an aperture plate 201 having two or more apertureopenings. The aperture plate 201 can be biased to a decelerationpotential. Thereby, the deceleration of the aperture plate 201 incombination with an acceleration of the detection elements 222 areconfigured for a separation and focusing of the secondary particles,e.g. the secondary electron beam. In light of the two or more apertureopenings, the separation of the secondary beam on different detectionelements can be provided. According to typical embodiments, the apertureplate 201 has a central aperture opening 202 and at least two radiallyouter aperture openings 204. Typically, four outer aperture openings 204can be provided.

According to typical embodiments, the secondary optics 200 includes theaperture plate 201 with a single central aperture opening or holesurrounded by a group of at least 4 outer aperture openings or outerholes. Thereby, the center can e.g. be being defined by the optical axisof the signal beam bundle. The plate can be arranged perpendicular tothis optical axis. Detection elements 222 of detector assembly 220 arepositioned behind the plate, e.g. in a plane parallel to the aperture.

According to typical operation conditions for a topography measurementmode, the signal beam, e.g. the SE bundle, is made slightly divergentand the plate is biased such that the SE are decelerated while theyapproach the plate. When the electrons are slow, they are easilydeflected towards the aperture openings in the plate, which means thatthe SE bundle is split into a central portion (low angle SE) and a groupof at least 4 outer bundles, corresponding to SE with large polarstarting angles and grouped around at least 4 azimuthal directions.After passing through the aperture openings, the secondary particles areaccelerated again to a significantly higher energy, e.g. a similarenergy, which the secondary particles have before entering into thedecelerating field of the aperture plate. According to typicalembodiments, the secondary particles can have an energy of about 20 keVto 50 keV, e.g. 30 keV, before deceleration. They are decelerated to anenergy of 100 eV to 15 keV, e.g. 5 keV, when passing through theaperture plate. Thereafter, they are accelerated to an energy of about20 keV to 50 keV, e.g. 30 keV, towards the detection elements 222. Thisacceleration has a focusing effect which allows for concentrating theseparated bundles on the small detection elements. The distribution ofthe secondary particles, e.g. the secondary electrons of the signalbeam, behind the aperture plate is not just a projection of the holes inthe aperture plate: the deceleration deflects the secondary particles tothe holes that would otherwise just hit the plate and get lost; theaccelerating field between the aperture plate and the detection elementsconcentrates the individual bundles of the signal beam, which wouldwithout the biasing of the aperture plate and the detection elements betoo large for a small high speed sensor.

According to yet further embodiments, an additional control electrode ofsimilar design as the decelerating aperture plate can be used to finecontrol the trajectories. Thereby, according to some embodiments, anelectrode similar to the electrode shown in FIG. 2B could be used. Theadditional control plate could operate as a focusing device. However,using the design shown in FIG. 2D, the plate 203 can be operated as adeflection device to align the individual bundles radially to thesensors by applying a positive or negative bias. Thereby, according tosome embodiments, plate 203, which can be configured to be biased,and/or deflection elements 302, such as pole pieces or electrodes, canbe provided. Deflections electrode can thereby move the beam radially.Recesses 303 can be provided to shape the field for adjusting thebundles to the detection elements. Both options, i.e. plate 201 andplate 203 are illustrated in FIG. 3B, wherein the additional controlelectrode is depicted with an inner portion being dotted to be similarto the aperture plate 201, whereas without the dotted part across-section similar to the design of FIG. 2D is obtained.

According to some embodiments, which can be combined with otherembodiments described herein, a secondary particle optics 200 as shownin FIG. 2B can be provided. The central aperture opening 202 in theaperture plate 201 corresponds to the central detection element 222 ofFIG. 2C. The outer aperture openings 204 correspond to the outerdetection elements 222 in FIG. 2C. According to typical embodiments, thediameter or the corresponding dimension of the aperture openings can be1 mm to 4 mm for the central aperture opening 202. For the outeraperture openings 204 the diameter or a corresponding dimension can be 3mm to 10 mm.

As shown in FIG. 2E, the aperture plate 201 of the particle optics 200can also include aperture openings 204, which are not circular. Apertureopenings having a tangential elongation or being shaped in the form of aportion of a ring or the like can decrease the dead areas of theaperture plate 201, i.e. the areas where signal particles, e.g. signalelectrons, can not pass through the openings in the plate. As furtherillustrated in FIG. 2E by the dotted lines of inner opening 202, theinner opening can be optional. Accordingly, only outer openings might beprovided according to some embodiments, which can be combined with otherembodiments described herein. In such a case it is also possible toincrease the radial length of the openings 204. An aperture plate withouter openings 204 only, can be used for topography measurements, eitherwith or without additional energy selection.

According to different embodiments, the first opening and/or the atleast one second opening in the aperture plate 201 can have a shapeselected from the group consisting of: a round opening, a portion of asector of the aperture plate, e.g. a sector of an annulus, or a similarshape. Thereby, round openings can be considered in light of theirbeneficial focusing properties of the signal beam bundles. Other shapesmight result in smaller dead areas within the aperture plate and, thus,a better collection efficiency of signal particles.

As shown in FIG. 2C, the detector arrangement 220 has five detectionelements 222, which correspond to the areas of the secondary beam optics200 shown in FIG. 2B. According to typical embodiments, which can becombined with other embodiments described herein, five areas andcorresponding detection elements 222 are provided. Thereby, a centralarea and a central detection element and four outer areas and four outerdetection elements can be provided. Accordingly, the secondary particlesreleased from specimen can be discriminated by the starting angle, i.e.whether the central detection element detects the secondary particle oran outer detection element detects the secondary particle. Further,separation of the direction of the starting angle can be provided forthe larger starting angles, which correspond to an outer area. Thereby,depending on which of the outer detection elements or channels of thedetector arrangement measures the secondary particles, the direction ofthe starting angle can be determined.

FIG. 2C further illustrates the size of the detection areas, which areindicated by reference L, as compared to the gap G between the activedetection areas. Accordingly, the detector arrangement 220 has deadareas between the active areas of the detection elements. As describedabove, this is due to the size of the active area of the sensorcorresponding inversely to the bandwidth of the detector arrangement.

As shown in FIG. 3A, the secondary particle optics 200 can include theaperture plate 201 and additionally the focus lens 301 configured forfocusing the secondary particles. Thereby, as illustrated in FIG. 3A,the generally divergent secondary particle beam can be focused to passthrough the aperture plate 201 at the central aperture opening 202 andto be detected at the central detection element 222.

According to yet further embodiments, which can be combined with otherembodiments described herein, as shown in FIG. 3B, the focus lens 301can be switched off or can be operated such that the secondary particlesare formed to a beam diameter adapted to the size of the apertureopenings in the aperture plate 201. Thereby, the secondary particlespass through all of the aperture openings. In light of the above,topography contrast and central BF imaging can be realizedsimultaneously (multi perspective imaging).

According to embodiments described herein, the detection device cananalyze the angular and energetic information contained in a bundle ofsecondary particles, e.g. SEs. Thereby, the energetic information can beprovided by biasing the aperture plate to a potential such that onlyparticles with a sufficiently high energy can pass through the apertureopenings of the aperture plate. The focus lens 301 allows for adjustingthe opening angle of the signal beam. The beam can be made divergent orconvergent as required. Thereby, collection efficiency of secondaryparticles can be improved. Further, switching between a topographyimaging mode and an energy filtered imaging mode can be provided.

Accordingly, embodiments described herein can relate to operation of thefocusing lens, wherein the divergence of the secondary particle beam ischanged due to the focusing lens. For one operational mode thedivergence of the beam can be adapted such that the beam has a beamdiameter at the aperture plate resulting in essentially a maximum ofsecondary particles passing through at least one of the apertureopenings, i.e. the inner or one of the outer aperture openings. In thisoperation mode, the signal particles, e.g. the signal electrons, can bedetected dependent from their starting angle. In another operationalmode the divergence of the particle beam is changed due to the focusinglens such that essentially all secondary particles, e.g. secondaryelectrons pass through the inner aperture opening. Thereby, all signalparticles are detected with one detections element 222.

According to embodiments described herein, the particle optics andparticularly the aperture plate 201 is provided as shown in FIGS. 5, 6Aand 6B. Thereby, the performance of basic aperture plates, as e.g. shownin FIG. 4, can be improved with regard to various aspects. As shown inFIG. 4, the aperture plate 201 with 5 holes (202 and 204, respectively)has a cross section with blocking or solid areas, which are ratherlarge. The dashed circle indicates the cross section of the impinging SEbundle.

As shown in FIG. 5, and according to some embodiments, which can becombined with other embodiments described herein, the aperture plate501, which is a part of the particle optics 500 configured for signalparticles, has and outer region 503, e.g. a circular body. The areabetween the holes 504 is provided by division bars 505. Accordingly, thearea between the holes is reduced to be more narrow. A central hole 502is provided, e.g. with a pincushion shape. According to embodimentsdescribed herein, the hole having the pincushion shape is alternativelydescribed as having concave portions, i.e. portions that are bendedinwardly towards the center of the opening. Thereby, the potentialdistribution in the outer holes can be smoothened, which leads to betterfocusing properties, particular of the outer holes. According to someembodiments described herein, the outer holes 503 are defined at leastat two sides by a bar, e.g. a division bar 505. Accordingly, the outerholes have a straight boundary at a length of at least 30% of theirperimeter. According to yet further embodiments described herein, whichcan be combined with other embodiments described herein, the centralhole 502 has at least two, typically at least four concave regions inthe perimeter, e.g. has a pincushion shape.

In light of the above, it is possible to provide a reduction of the lossof signal electrons at the aperture plate from typically about 30% toless than 5%. This is inter alia achieved by reducing the head-oncross-section of the device. That is, embodiments described herein, havea reduced area with solid material in the cross-section.

In spite of the abandonment of a circular design of openings, a goodfocusing of the beamlets can be achieved by shaping the geometry suchthat the electrostatic potential of the sub-lenses is nearlyrotationally symmetric and/or by applying a strong decelerating field infront of the device and a strong accelerating field after the beamseparator. Good focusing increases the operating window when largediameter pin diodes are used and/or allows for the use of smaller pindiodes, thus enabling increased detector bandwidth.

According to yet further embodiments, which can be combined with otherembodiments described herein, and as shown in the figures herein, theaperture plates 201, 501 and 601 have a thickness of at least 5 mm. Thethickness is provided by an extension in axial direction or in directionof the optical axis of the signal particles. Typically, the thickness orextension in axial direction or in direction of the optical axis of thesignal particles is from 10 mm to 20 mm. Thereby, an increasedseparation of the beamlets can be provided. Typically, a separation of10 mm between the central beamlet and the outer beamlets can beachieved. This allows for the utilization of standard pin diodes with 5mm diameter and enables a feasible design of the sensor element. Yetfurther in light of the fact that the reach-through of the acceleratingfield between aperture and sensor is influenced by the thickness of theplate, a reduction of operating voltage is a beneficial side effectcoming from the elongation of the device, i.e. a minimum thickness orminimum extension in axial direction or in direction of the optical axisof the signal particles. This helps to achieve better high voltageimmunity, reliability and stability and enables a feasible design of thedevice.

According the present disclosure, the aperture plates 201, 501, and 601are described as a plate with a minimum thickness. Alternatively, theaperture plates could also be described as tubes and these terms can beused exchangeably. However, as the radial dimension is typically largerthan the axial dimension mostly it is referred to as aperture plates.Yet, references to tubes or tubular structures herein, take intoconsideration the minimum thickness of the plate according to someembodiments.

As shown in FIGS. 6A and 6B a further additional or alternativemodification can be provided by an adjustable separation of thebeamlets. This provides a fine adjustment which allows to always centerthe beamlets to the sensors. According to embodiments described herein,an adjustable separation can be provided by splitting the outer region(see, e.g. 503 in FIG. 5) or the outer tube of the beam separator, i.e.the aperture plate. Accordingly, some embodiments include a division bar605 for separating the openings 604, first outer portions 601 and secondouter portions 611. For example, the first outer portions 601 can have aT-shaped cross-section in combination with the division bars 605.Thereby, a central cross-shaped section including at least four T-shapedstructures is provided. The central hole 602 is provided essentially inthe center of the cross-shaped section. Four T-shaped structuressurround the central opening 602, wherein each T-shaped structure isprovided by a division bar 605 and a first outer portion 601.

The central cross shaped portion is biased to V_(foc). This isillustrated in FIG. 6A, wherein power supply 631 is connected to thecentral cross shaped portion. The four second outer portions 611, e.g.the four additional deflection plates (one per outer beamlet), can bebiased to ±ΔV with respect to the central part of the device, i.e. thereis a non-zero voltage, which is positively or negatively added to thepotential of the central part. A second power supply 632 is provided toprovide a voltage to the second outer portions or an offset voltage withrespect to the voltage of the first power supply to the second outerportions 611. Accordingly it is optionally possible to create an inwardor outward deflection of the outer beamlets.

Even though the central portion is described as cross-shaped, whichcorresponds to the four openings 604 shown in FIGS. 6A and 6B, threeopenings, five openings, six openings or an even higher number ofopenings results in a corresponding shape of the central portion and isto be considered a yet further modification of the embodiments describedwith respect to FIGS. 6A and 6B.

The embodiments described with respect to FIGS. 6A and 6B add anotherdegree of freedom to the biasing of the aperture plate 601. Althoughfocusing and beam separation are generally linked to each other, thedesign of the device allows to change the mutual separation of thebeamlets without unacceptable deterioration of the focus. This can beused to compensate variations in SE energy or angular distributioncaused by variations in column operation, e.g. different landingenergies of the primary beam, changes in extraction field, localtopography and the like.

According to some embodiments, as described above, the thickness of theplate can be adjusted to determine the reach-through of the acceleratingfield between aperture and sensor. According to yet further additionalor alternative embodiments, the above-described additional features onthe aperture plate, e.g. on the side facing the decelerating field, canbe arranged in order to influence the spatial distribution of thedecelerating field. According to yet further additional or alternativeembodiments, the ratio of the aperture diameters of the inner apertureopening, e.g. central aperture opening, and the outer aperture openingcan be varied. According to typical examples, the diameter of the outeraperture openings can be at least 2 times the diameter of the inneraperture opening. However, this value might be dependent of the numberof outer aperture openings. That is, the higher the number of outeraperture openings, the smaller above-described diameter ratio. Forexample, if the aperture plate would contain a large number of identicalholes in a regular pattern, e.g. a hexagonal pattern, the ratio woulddrop to 1. According to typical embodiments, the aperture openings canbe round or can have any other desired shape such as a shape of aportion of an annulus, a ring or the like.

According to some embodiments, which can be combined with otherembodiments, four outer aperture openings can be provided. Thereby, thedetection device is sensitive to topography in two orthogonaldirections. This also relates to the fact that wafer structures have twodistinct perpendicular directions. According to typical operationmethods, the detector can be rotated to a first angle to get maximumsensitivity for the desired topography of the object to be imaged, e.g.,the wafer structures. Further, the detector can be rotated by 45 degreesas compared to the first angle in order to suppress the signal from theregular structures and enhance the defect contrast. Thereby, accordingto yet further implementations thereof eight outer aperture openings canbe utilized. By choosing the rotation angle of the detector as describedabove, every second aperture opening (e.g. openings #1, 3, 5 & 7) andcorresponding detection elements of eight outer detection elements candetect regular structures of an object to be imaged, while theinterjacent aperture openings (e.g. openings #2, 4, 6 & 8) andcorresponding detection elements would be sensitive to defects. Theabove variations can be independently or in combination be utilized toobtain a high detection efficiency, i.e. low loss of secondary particleson the splitting aperture and low loss of secondary particles on thedetector, as well as good discrimination of the secondary particlesdepending on the starting angle.

According to some embodiments, the detection device can be switchedbetween a topography measurement mode and a one-detection-channel mode.A 100% BF image can be produced. Thereby, the deceleration can beswitched off by biasing the aperture plate to the potential of thesignal beam. Further, the focus lens 301 is controlled to focus the beamso that it can completely pass the central aperture 202 for detection onthe corresponding central detection element 222. According to a yetfurther operational mode, the signal beam can be focused towards thecenter of the central aperture opening and a decelerating voltage can beapplied to the aperture plate. Thereby, an energy filter can beprovided, wherein only signal particles with a sufficiently high energycan pass through the aperture opening. Signal particles for which thedeceleration gets too strong are reflected at the aperture plate.Accordingly, an energy filter can be provided. Similarly, the topographyoperational mode utilizing also the outer aperture openings, which isdescribed above, can be combined with energy filtering by raising thedecelerating voltage of the aperture plate until the signal particleswith lowest starting energy are reflected. Accordingly, only signalparticles with larger starting energy can pass through one of theopenings in the aperture plate to be accelerated towards a correspondingdetection element and be detected for signal generation.

As described above, the particle optics 200 according to embodimentsdescribed herein, splits the signal beam, e.g. the SE bundle, into aplurality of smaller bundles. For example, this can be a central, innerbundle (SE with low starting angle) and a number 1, 2, 4, 8 or evenmore, outer bundles with high polar starting angles. Thereby, eachpartial bundle can be centered around an average azimuthal angle.According to typical implementations, the number of outer bundles can atleast be 4 to obtain topographic sensitivity in 2 dimensions. However,higher numbers are also possible.

According to embodiments, described herein, the bundles, i.e. theportions of the signal beam, are detected using individual detectionelements of a detector assembly. The detection elements are spatiallyseparated by a gap G as illustrated in FIG. 2C. For example, thedetection elements can be the electron detectors (pin diodes,scintillators etc). Accordingly, closely arranged detection elements,e.g. segmented pin diodes or the like can be avoided. Thereby, problemsrelated to the pin diode area that separates the active segments, suchas charging, signal loss, and/or cross-talk can be avoided. The highprice and complicated development cycles of segmented detectors can beavoided. Yet further, there is an increased flexibility in sensordesign, which can also result faster time-to-market cycle.

According to embodiments described herein, the secondary beam optics 200is utilized for charged particle beam devices, wherein a secondary beamor signal beam is separated from the primary beam, i.e. the primary beambeing guided on the specimen for impingement of the primary beam thereonand the resulting generation of the signal beam or secondary beam.

There are two principle methods for separating the primary and secondaryelectron beams, both of which take advantage of the fact that the forceon a moving electron traversing a magnetic field is dependent upon theelectron's velocity. This is a fundamental principle described by theLorentz force law. Since the primary electrons and secondary electronsare essentially traveling in opposite directions, the force acting uponthe two bundles will be opposite in direction when traveling through atransverse magnetic field.

One possible beam separator is the Wien filter. A Wien filterarrangement in accordance with an embodiment of the invention is shownschematically in FIG. 7A. An emitter 205 emits a primary-electron beam130 which passes through Wien-type momentum-dispersive filter 215 and isfocused by objective lens 10 on a sample 125. Secondary-electron beam140 passes through objective lens 10 and Wien-type filter 215 in adirection opposite to that of primary-electron beam 130. The Wien filtercan be adapted such that the primary-electron beam 130 passes unaffectedby Wien filter 215, while secondary-electron beam 140 is bent as itpasses through Wien filter 215 so that it exits the column inclined withrespect to primary-electron beam 130. Once separated from theprimary-electron beam, the secondary electrons can be focused andfiltered, e.g., by secondary-electron optics 200, a charged particleunit for deflecting and focusing charged particles, without any effecton the primary-electron beam. Electron detector 220 detects thesecondary electrons and produces a secondary-electron signal 145 foreach of the detection elements 220, i.e. for each of the detectionchannels. Though the primary beam and the secondary beam actually occupythe same physical space above the specimen plane, they are drawn asseparate arrows in FIG. 7A for convenience of illustration.

The Wien filter uses crossed electric and magnetic fields, theamplitudes of which are adjusted so that there is zero net force on theprimary beam and a deflection (transverse) force on the secondary beam.

Schematic views of the usage of a Wien filter 215 are further shown inFIGS. 7B and 7C. Thereby, the electric and magnetic fields within theWien filter are adjusted such that in FIG. 7B the primary chargedparticle beam is unaffected. Contrary thereto, within FIG. 7C theelectric and magnetic fields are adjusted such that the secondarycharged particle beam is unaffected. Nevertheless, both embodimentsutilize the separation of the primary and secondary beam. Thus, focusingor filtering can be applied to the beam of secondary charged particleswithout influencing the primary charged particle beam. According to afurther option as shown in FIG. 7D it is further possible that bothbeams are deflected to some degree, whereby a beam separation isachieved. For example, according to some embodiments, which can becombined with other embodiments described herein, an achromatic ½ ExBWien filter can be provided. Thereby, the primary beam can beachromatically deflected and the primary beam and the secondary beam areseparated.

Another method of separating the primary and secondary beams is to usemagnetic deflection without an electric field. FIG. 8A showsschematically an arrangement of magnetic-beam separator optics inaccordance with an embodiment of the invention. Emitter 205 produces aprimary-electron beam 130 which is first deflected by the first magneticdeflector 415 such that primary-electron beam 130 enters a secondmagnetic deflector 420 at an angle. To keep the effect of the magneticbeam separator on the primary beam small, the angle of deflection in thefirst magnetic deflector 415 should be kept below 10 degrees.Primary-electron beam passes through the second magnetic deflector 420and is directed at specimen 125. Secondary electrons of beam 140 arethen deflected by the second magnetic deflector 420 such that the totalangle α of separation of primary beam 130 and secondary beam 140 isroughly twice that of the deflection of the primary beam in the firstmagnetic deflector 415 (15-20 degrees). This separation is enough toallow for a beam bender, sector 440, to be mechanically isolated fromprimary beam 130 and to be made strong enough to deflect secondary beam140 so that the secondary electrons are now traveling with a largeangle, that is between 30° and 100°, with respect to the primary beam.

Generally, sectors that might be combined with the embodiments disclosedherein might be electrostatic, magnetic or combinedelectrostatic-magnetic. Since the space required for an electrostaticsector is smaller than the space for a sector including a magnetic part,typically an electrostatic sector is used.

Following sector 440, which already has conducted a reduction ofdivergence (focusing) at least in one dimension, is a set ofsecondary-electron optics 200 which additionally focuses and deflectsthe secondary beam depending on the starting angle of the secondaryelectrons. Noteworthy is that this configuration may result in a shiftedcolumn; that is, the upper portion of the primary beam optics (e.g.,emitter 205 and part 1 magnetic deflector 415) is shifted laterally fromthe lower portion (e.g., part 2 magnetic deflector 420 and objectivelens 10). Thus, emitter 205 does not have line-of-sight view of specimen125. After passing through secondary-electron optics 200,secondary-electron beam 140 is detected by electron detector assembly220 to produce a secondary-electron signal 145 for each of the detectionelements or each of the detector channels respectively.

To achieve large angle beam separation a beam bender or sector after thebeam separator can be used. The primary beam is completely shielded andtherefore unaffected by the sector fields. Sector 440 can be eitherelectrostatic, magnetic or both. An electrostatic beam bender is usedwhere space is a consideration.

FIG. 8A refers to the specific embodiment realized with a magneticdeflector affecting the primary and the secondary charged particle beam.FIGS. 8B to 8C show schematically applications which can be realized ingeneral. These beam paths may be combined with any other details ofother embodiments.

Therein, a magnetic deflector 420 is shown. Within FIG. 8B the primarycharged particle beam enters the magnetic deflector under a definedangle of incidence; and is deflected towards a specimen. The beam ofsecondary electrons, which are released from the specimen, enters themagnetic deflector on its way back towards the optical column and isdeflected such that the primary charged particle beam and the secondarycharged particle beam are separated. The magnetic deflector 420 acts asa separating unit between the primary and the secondary charged particlebeam.

The general usage shown in FIG. 8B can be applied for differentembodiments that are shown in FIGS. 8C and 8D. In FIG. 8C, the gun 405emitting the electrons is tilted with respect to the electron directionon impingement on a specimen. If a parallel primary electron beamdirection of emitted electrons and of electrons impinging on a specimenis required, a further magnetic deflector 415 may be used to compensatefor the beam-tilt introduced by magnetic deflector 420. Again, theseschematic beam paths can be combined with any other embodiments showingfurther details of the charged particle optics.

Further embodiments will be described with respect to FIGS. 9A and 9B.FIG. 9A shows a sector 440. Sector 440 has a negatively-charged U-bend535 and a positively-charged U-bend 525 serving to bend the electronbeam. Optionally, a pair of sector side plates can be provided. Thereby,the electron beam is focused in one dimension and, additionally, is keptat a high energy to avoid time of flight effects which may have impacton high-speed detection. A focusing in the second dimension takes placein quadrupole element 545. Thereby, the sector 440 and the quadrupoleform a double-focusing sector unit. Further, it may be possible to use acylinder lens instead of a quadrupole to obtain double focusing.

The electron beam enters secondary beam optics 200 as described herein.Thereafter a detection at high speed and including a topographyinformation correlated to the starting angle can be detected by detectorassembly 220.

In the further embodiment of FIG. 9B a hemispherical sector 570 is used.In view of the hemispheric shape the electron beam entering the sectoris focused in both dimensions. Thus, no additional focusing unit isrequired for the double-focusing sector unit 570. The secondaryparticles result in signal generations as described above.

According to yet further embodiments, which can be combined with otherembodiments described herein, FIG. 9B further illustrates voltagesupplies 992, 994, and 996. Voltage supply 992 is connected to apertureplate 201 for biasing thereof. Thereby, a deceleration field asdescribed above can be provided. According to typical examples, thedeceleration field can correspond to a decrease of particle energy ofabout 20 keV to 30 keV. Voltage supply 994 is connected to detectionelements 222 in order to accelerate the secondary particles towards thedetection elements 222. Thereby, also a focusing is provided. Theacceleration field can correspond can correspond to an increase ofparticle energy of about 20 keV to 30 keV.

According to a further embodiment (not shown) the focusing of the doublefocusing sector unit (440, 545 in FIG. 9A or 570 in FIG. 9B) can beassisted with an additional focusing unit. Thus, the double focusingsector unit may also include additional lenses, for example anEinzel-lens. This additional lens may also be applied to move the focusof the sector to a position corresponding to the position of the filter,e.g. the potential saddle formed in the central opening of the apertureplate.

A further aspect will now be described with respect to FIG. 9C, whereinthe detection optics according to one embodiment is shown. FIG. 9Cincludes a sector 440 acting as a deflection angle increasing unit. Thebeam of secondary electrons, which has already been separated from theoptical axis by an angle of for example 3° to 15°, is further deflectedtowards detector assembly 220.

Generally, an electrostatic beam bender can be either cylindrical orhemispherical. The cylindrical type suffers from the fact that as thebeam is bent the secondary electrons are focused in one plane and not inthe other. A hemispherical beam bender focuses the secondary beam inboth planes. The cylindrical sector can be used with side plates biasedto achieve focusing in the transverse plane, yielding similar focusingproperties than the hemispherical sector.

FIG. 9C is a schematic view of such a cylindrical sector. Side plates(not shown) can be positioned—with respect to the perspective of thisfigure—in front of and behind the gap between the sector electrodes 525and 535. According to typical embodiments, a first cross-over of thesignal beam is provided essentially within the objective lens 10 orshortly thereafter. A second cross-over of the signal beam is typicallyprovided after the sector 440. A third cross-over can be provided,depending on the operation mode (see, e.g. FIG. 3A) by the focusingaction of the focusing lens 301.

According to yet further embodiments, which can be combined with otherembodiments described herein, the particle optics 200 can includefurther elements as illustrated in FIG. 9C. Particularly for EBIapplications and other applications with a larger field of view wherethe scanning of the primary electron beam influences the detection, e.g.scanning areas of 50 μm×50 μm and above, further optical elements can beutilized for the secondary optics 200. Thereby, the particle optics canshape the signal beam, e.g. the SE bundle, before the signal beam entersthe beam splitting aperture plate 201. According to typical embodiments,which can be combined with other embodiments described herein, theparticle optics can include the focus lens 301 and/or one or moredeflection assemblies 901/903.

According to some embodiments, a focus lens can be provided. The focuslens focuses the signal beam on the central detection element togenerate a bright field image. Alternatively, the focus lens focuses thesignal beam onto a potential saddle in the central aperture, while theaperture plate is biased by a bias voltage to generate an energyfiltered image. According to yet another alternative, the focus lens 301can make the signal beam divergent or can adjust the divergence thereofsuch that the diameter of the signal beam is adjusted to the diameter ofthe decelerating aperture plate. Accordingly, the focus lens can be usedto switch between different operation modes, i.e. imaging modes.

According to yet further embodiments, which can be combined with otherembodiments described herein, the particle optics 200 can furtherinclude one or more deflection assemblies. Thereby, the deflectionassemblies 901 and 903 can be controlled for aligning the signal beam,e.g. the SE bundle to the aperture plate. Additionally or alternatively,the deflections assemblies can be controlled for de-scanning the signalbeam. That is a deflection (de-scan, anti-scan or counter-scan) isprovided for compensating a movement of the signal beam which resultsfrom scanning of the primary beam, which generates the signal beam onimpingement on a specimen.

According to typical embodiments, Anti-scan can particularly be appliedin systems with a large field of view (FOV). For large FOV, e.g. of 100μm×100 μm and above, the scan of the primary beam also deflects thesignal beam. Without compensation thereof, this deflection of the signalbeam results in a movement of the signal beam on the detector, whichmeans that the detection result will not be uniform but will depend onthe beam position in the FOV. Such a movement will particularly benoticeable, when the entire particle optics, which influences the signalbeam (e.g., including the objective lens, a beam splitter, a beam benderand a focus lens) magnifies the image scan movement onto the detectionelement.

According to typical embodiments, for each of the deflection assemblies901 and 903, a set of at least 4 deflection plates can be provide thatcan be connected to deflection voltages. The deflection voltages can besynchronized with the image scan of the primary beam and amplifiedand/or rotated such that deflection of the signal beam generated byprimary beam scanning cancels the motion of the signal beam in thesensor plane.

According to some embodiments, a deflection assembly, e.g. a de-scandeflector, can be arranged immediately in front of the suggesteddetector assembly to keep the optical axis of the SE bundle fixed on thecenter of the central opening, independent of the PE beam position onthe wafer. According to typical examples, a de-scanning can, however,also be provided as early as possible after secondary particlegeneration. This establishes a constant axis for the signal beam, whichcan thus be more easily aligned to the focus elements of the signalbeam. Accordingly, aberrations for the signal beam due to focusing ofthe signal beam while the signal beam is travelling off-axis of afocusing elements can be avoided.

As shown in FIG. 9C, the first deflection assembly 901 can de-scan thesignal beam and align the signal beam to the focus lens 301. Thedeflection of the first deflection assembly 901 can introduce a beamtilt with respect to the optical axis of the signal beam. This beam tiltcan be compensated for by the second deflection assembly 903. The seconddeflection assembly can further improve alignment on the aperture plate201.

A secondary electron beam 140 passes through an opening 410 in anobjective lens 10 and an opening in a plate 520 to enter a sector 440.Sector 440 has a negatively-charged U-bend 535 and a positively-chargedU-bend 525 serving to bend the secondary-electron beam 405. Further, apair of sector side plates are provided. Secondary electron beam 405 isthen aligned as it passes through an SE alignment quadrupole element 445and focused as it passes through an SE focusing lens 450. Secondaryelectron beam 405 then passes through openings in grounded plate 455 andin SE optics 200 to an electron detector assembly 220.

A drawback of the cylindrical sector without side plates is that itfocuses the SE beam in one plane (up and down on the page) and not theother (in and out of the page). This lack of focusing can be compensatedby placing electrodes on the sides of the cylindrical sector to forcefocusing action in this plane. There are two motivations for uniformfocusing action by the sector. One is to provide for a small spot on thehigh-speed detector and the other is to enable good energy filteringbecause the filter is sensitive to both energy and direction of thesecondary beam.

Thus, the filter should be located approximately in a focus of thesecondary electrons.

FIG. 10 is a schematic illustration of a wafer inspection system 900 inaccordance with an embodiment of the invention, employing anelectron-optical subsystem as described above with reference to FIGS.2-6. An electron beam column 902 includes an e-beam source 904, magneticbeam separator 906 and objective lens 908 for applying a primary beam910 to a wafer 912 carried on an x-y stage 915. Secondary electrons fromwafer 912 pass through beam separator 906, sector 914, and focusing anddeflecting elements 200 to detector 220. The signals from detector 220are supplied to imaging electronics 920.

Wafer 912 and stage 915 are contained in a vacuum chamber 922 supportedon an isolation frame 924. Vacuum pumps 926 maintain a suitable vacuumin the chamber 922 and column 902 during operation. Wafer 912 is placedin and removed from chamber 922 by a wafer handler subsystem 928.

Wafer inspection system 900 is controlled by a computer system 930having a control processor, image processor and image memory, forexample. Computer system 930 is in communication with a workstation 932having input/output devices 934 such as a keyboard and a pointing deviceor other suitable devices permitting human interaction, and a display936. Control processor 930 communicates via a bus 938 with controlcircuits such as PE-beam control 940 which regulates theprimary-electron beam 910, SE optics control 942 which controls thefocusing and deflection elements of column 902 to provide a suitablesecondary-electron beam on detector 220, PE alignment and deflectioncontrol 944 which controls the application of primary beam 910 on wafer912, vacuum pumps control 946 for controlling vacuum pumps 926, wafervoltage control 948, stage control 950, and handler control 952. Controlprocessor 930 also receives imaging data via bus 938 from imagingelectronics 920 for storage, processing and image analysis.

To provide for greater throughput than is possible with single-columnsystem, multi-column systems are also contemplated. FIG. 11 showsschematically a multi-column e-beam wafer-inspection system 1000 havinga row 1005 of e-beam columns 1010, 1015, 1020 to enable simultaneousinspection of multiple regions of a wafer 912.

Within FIG. 11, a multi-column device including three sub-units isshown. As will be understood by a person skilled in the art any suitableother number can be applied. For example 5, 10 or 15 electron beams canbe arranged in a row.

Further, it is possible to position several rows next to each other.Thereby, an array of electron beams impinging on a specimen is realized.In order to have sufficient space for the separated charged particlebeams, for example two rows can typically be arranged next to eachother. Nevertheless, if no space-restrictions are present, 3, 5 or anyother suitable number rows may be applied as well.

For arranging several sub-columns in a line, in an array or otherpattern, some of the components, that usually are individually acting ona single electron beam in the case of a single-beam column, may becombined. Thus, one emitter array emits all electron beams or oneobjective lens focuses all beams of the multi-beam device. Examples aregiven in the following.

A further embodiment arraying multiple beams is shown in FIG. 12.Therein, additionally multi-apertures are provided for each beam. Thus,different apertures can be selected using deflectors. Additional detailsrelating to the selection of aperture openings of multi-apertures, asdisclosed in European Application Nr. 03 00 6716 assigned to the sameassignee as the present application, may also be utilized.

Device 130 has a housing 131 and a specimen chamber 135. The housing aswell as the specimen chamber can be evacuated through vacuum ports.Within the specimen chamber, specimen 13 is located on specimen stage136, which can move the specimen independently in two directions. Forcontrol of the specimen, movement control unit 136′ is connected tospecimen stage 136. Each of the four electron beams 12 has its ownoptical axis 11. The beams are emitted by an emitter array 132. Theemitter array is controlled by control unit 132′, that is, the beamcurrent, the anode potential and a possible synchronization of theelectron beams with the scanning over specimen 13 for each electronbeam, respectively, is controlled. A multi-lens system 133 including anEinzel-lens module for each electron beam is used as a condenser lensfor the four charged particle beams. The lens system 133 is controlledby control unit 133′. The control units can be connected to a commoncontrol 139.

Generally, without referring to the embodiment of FIG. 12, a single-beamor multi-beam column has typically at least two focusing elements foreach primary electron beam. It is advantageous if the lenses (or atleast one) are immersion lenses to allow the electron beam to be on ahigher potential (beam boost potential) between the lenses. Further,according to one alternative, a combined gun-condenser lens is preferredfor shaping the emitted beam.

For focusing the electron beams on specimen 13, a magnetic electrostaticcompound lens 134 for all electron beams is used. Thereby, magneticsub-lenses share a common excitation coil and for each electron beam anelectrostatic sub-lens is integrated in the compound lens. Thecomponents of the magnetic electrostatic compound lens are controlled bycontrol unit 134′.

Within FIG. 12, the electrostatic lens 133 and the magneticelectrostatic compound lens 134 are used exemplarily. Instead, twoelectrostatic-lenses could be used, namely as a condenser lens and as anobjective lens. Alternatively, two magnetic electrostatic compoundlenses could be used, namely as a condenser lens and as an objectivelens. However, it is also possible that no condenser lens is requiredand only one multi-beam lens is used. Thereby, an electrostatic lens ora magnetic electrostatic compound lens could be used. Further, aproximity electrode 82 and a respective control unit 82′ are provided,whereby an extraction field corresponding to each of the four electronbeams is realized. Additionally, for each electron beam 12, electrodes137 for providing a beam boost potential are provided. Beyond theabove-mentioned components, a deflection-switch system is provided foreach electron beam.

Contrary to the magnetic deflection systems shown in FIGS. 8A to 8D, thecombination of 4 deflectors allows for an optical axis of the objectivelens sub-units that is in common with the optical axis of the emittersub-units. First deflection stages 14 deflect electron beams 12 to theleft or to the right, depending on the kind of aperture used withinaperture unit 41. For each electron beam, aperture unit 41 includes alarge aperture for a high current measurement mode and a small aperturefor a high resolution measurement mode.

Secondary electrons are separated from the primary electron beams bysectors 440, which are provided for each electron beam. The beamseparation of the schematic drawing of FIG. 12 is illustrated within theplane of the figure. This is done for the sake of easier drawing only.Generally, the beam separation and thus, the arrangement of thedetection units can also be realized in a dimension orthogonal to theplane of the figure.

For detection of the secondary electrons a focusing and deflectionoptics 200 is provided. All detection units are controlled by controller16′/44′, whereas each deflection stage 14 is controlled by control unit14′.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A secondary charged particle detectiondevice for detection of a signal beam, comprising: a detectorarrangement having at least two detection elements with active detectionareas, wherein the active detection areas are separated by a gap; and aparticle optics configured for separating the signal beam into a firstportion of the signal beam and into at least one second portion of thesignal beam, and configured for focusing the first portion of the signalbeam and the at least one second portion of the signal beam, wherein theparticle optics comprises an aperture plate having at least a firstaperture opening in the aperture plate, and at least one second apertureopening in the aperture plate, wherein the first aperture opening has aconcave shaped portion bended inwardly towards the center of theopening.
 2. The detection device according to claim 1, wherein the firstaperture opening has a pincushion shape.
 3. The detection deviceaccording to claim 1, wherein the at least one second portion of thesignal beam is a second, a third, a fourth and a fifth portion of thesignal beam and the particles optics is configured for separating thesignal beam in the first to fifth portion.
 4. The detection deviceaccording to claim 1, wherein the at least one second aperture openingis at least one second radially outer aperture opening.
 5. The detectiondevice according claim 4, wherein the at least one second apertureopening is at least four outer aperture openings.
 6. The detectiondevice according to claim 1, wherein the second aperture opening has aperimeter with at least one straight boundary.
 7. The detection deviceaccording to claim 6, wherein the straight boundary is provided by adivision bar.
 8. The detection device according to claim 1, wherein theparticle optics further comprises: a focusing lens for focusing thesignal beam through the first inner aperture opening.
 9. The detectiondevice according to claim 1, wherein the detector arrangement furthercomprises: a voltage supply connected to the aperture plate andconfigured for providing a deceleration potential.
 10. The detectiondevice according to claim 1, wherein the particle optics furthercomprises: a first deflection assembly for compensating dislocations ofthe signal beam introduced by scanning of a primary charged particlebeam and for aligning the signal beam.
 11. The detection deviceaccording to claim 1, wherein the thickness of the aperture plate is 5mm or above.
 12. The detection device according to claim 1, wherein thedetection elements are PIN diodes having an active detection area of 1mm² or below.
 13. The detection device according to claim 1, wherein thedetector arrangement is configured to have detection elements providinga 45° angular resolution by providing at least 8 detection elements. 14.A charged particle beam device, comprising: a charged particle beamsource for providing a primary charged particle beam; a first focusingelement for focusing the primary charged particle beam on the specimen,wherein a signal beam is generated; and a charged particle detectiondevice for detection of a signal beam, comprising: a detectorarrangement having at least two detection elements with active detectionareas, wherein the active detection areas are separated by a gap; aparticle optics configured for separating the signal beam into a firstportion of the signal beam and into at least one second portion of thesignal beam, and configured for focusing the first portion of the signalbeam and the at least one second portion of the signal beam, wherein theparticle optics comprises an aperture plate having at least a firstaperture opening in the aperture plate, and at least one second apertureopening in the aperture plate, wherein the first aperture opening has aconcave shaped portion bended inwardly towards the center of theopening.
 15. The charged particle multi-beam device of claim 14,comprising at least two of the charged particle beam source, at leasttwo of the first focusing element, and at least two of the chargedparticle detection device.
 16. A method of operating a detection device,the method comprising: biasing an aperture plate of a particle optics,wherein the particle optics includes at least a first aperture openingin the aperture plate, and at least one second aperture opening in theaperture plate, wherein the aperture plate is biased such that onepotential is surrounding the first aperture opening and wherein thefirst aperture opening has a concave shaped portion bended inwardlytowards the center of the opening; detecting a signal beam with adetector assembly having at least one detection element corresponding tothe first aperture opening and at least one detection elementcorresponding to the at least one second aperture opening.
 17. Themethod according to claim 16, wherein the detecting is conducted with abandwidth of 1 GHz or above.
 18. The method according to claim 16, themethod further comprising focusing the signal beam.
 19. The detectiondevice according to claim 10, wherein the particle optics furthercomprises a second deflection assembly for compensation dislocations ofthe signal beam introduced by scanning of a primary charged particlebeam and for aligning the signal beam.
 20. The method according to claim16, wherein the first aperture opening has a pincushion shape.